From: gdavis@mvista•com (George G. Davis)
To: linux-arm-kernel@lists•infradead.org
Subject: [Kgdb-bugreport] [PATCH] ARM: change definition of cpu_relax() for ARM11MPCore
Date: Thu, 15 Apr 2010 13:36:09 -0400 [thread overview]
Message-ID: <20100415173609.GA29752@mvista.com> (raw)
In-Reply-To: <20100412173247.GA3048@n2100.arm.linux.org.uk>
Hi,
On Mon, Apr 12, 2010 at 06:32:47PM +0100, Russell King - ARM Linux wrote:
> On Mon, Apr 12, 2010 at 06:23:58PM +0100, Will Deacon wrote:
> > This patch changes the definition of cpu_relax() to smp_mb() for ARMv6 cores,
> > forcing the write buffer to drain while inside a polling loop on an SMP system.
> > If the Kernel is not compiled for SMP support, this will expand to a barrier()
> > as before.
If I've followed these threads [1][2] correctly, this ARM11 MPCore issue
was discovered while running the "KGDB: internal test suite" (KGDB_TESTS)
and that problem is resolved via "kgdb: use atomic_inc and atomic_dec
instead of atomic_set" [3]. If so, isn't the original ARM11 MPCore KGDB
cpu_relax() issue just a red herring? Shouldn't any polling loops
which depend on specific (hardware) write/read order implement appropriate
barriers rather than rely on cpu_relax() to guarantee order? If
perhaps there are indeed other cases where cpu_relax() is being used
incorrectly, then maybe those should be fixed instead? Just curious...
> Linus asked how expensive (in terms of power rather than performance)
> this was; so far that question has remained unanswered. Can someone
> please answer his question?
Thanks!
--
Regards,
George
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/010691.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/011076.html
[3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff_plain;h=ae6bf53e0255c8ab04b6fe31806e318432570e3c
next prev parent reply other threads:[~2010-04-15 17:36 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-12 17:23 [PATCH] ARM: change definition of cpu_relax() for ARM11MPCore Will Deacon
2010-04-12 17:32 ` Russell King - ARM Linux
2010-04-15 17:36 ` George G. Davis [this message]
2010-04-15 21:03 ` [Kgdb-bugreport] " Jamie Lokier
2010-04-16 13:54 ` Will Deacon
2010-04-19 14:39 ` Will Deacon
-- strict thread matches above, loose matches on Subject: below --
2010-03-09 16:06 Will Deacon
2010-03-09 16:22 ` Russell King - ARM Linux
2010-03-09 16:35 ` Will Deacon
2010-03-09 16:49 ` Russell King - ARM Linux
2010-03-09 17:59 ` Will Deacon
2010-03-10 22:06 ` [Kgdb-bugreport] " Jason Wessel
2010-03-11 2:47 ` DDD
2010-03-11 13:53 ` Will Deacon
2010-03-11 13:29 ` Will Deacon
2010-03-11 14:51 ` Will Deacon
2010-03-16 17:26 ` Will Deacon
2010-03-16 18:52 ` Jason Wessel
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